Expansion joint

Abstract

An expansion joint is described comprising a flexible, metal-free tubular connector having corners and sides, said connector joining the end of adjacent ducts, and with each corner comprising a central section and two expansion sections. As the expansion joint expands and contracts, the central and expansion sections of each corner extend and retract, changing in shape to accommodate the joint movement and to prevent stress concentrations at corners.

What is claimed is: 
     
       1. A flexible expansion joint for joining the ends of spaced-apart adjacent ducts, which comprises: a. a tubular connector having a specific configuration which includes: a plurality of corners; a plurality of sides each of which connects two of said corners; and terminal end portions adapted to mate with the facing ends of said ducts; and   b. means comprising a center section and two adjacent expansion sections incorporated in each of said corners with each of said sections extending axially of the connector to permit axial movement of said connector while maintaining a constant surface area of said connector.   
     
     
       2. The expansion joint of claim 1 wherein said center section and said expansion sections cooperate to permit said axial movement. 
     
     
       3. A flexible expansion joint for joining the ends of spaced-apart adjacent ducts, which comprises: a. a tubular connector having a specific configuration which includes: a plurality of corners; a plurality of sides, each of which connects two of said corners, and has a base; and terminal end portions adapted to mate with said ends of said ducts;   b. each of said corners comprising: i. a central section embodying one corner extremity of said expansion joint; and   ii. two expansion sections, each positioned between and abutting said central section and one of said sides, and each having a configuration comprising a center line coplanar with the plane of said base of the side of said joint which the other expansion section in said corner abuts; slope portions meeting at and extending from the center line to the extremities of said expansion section; and two ends, each of which is joined to a respective end of said central section and said other expansion section at the intersection of said bases of said sides meeting at said corner; and wherein     c. during extension or contraction of said connector each of said expansion sections varies in breadth but maintains a constant surface length, and the rate of change of curvature of said center line of said expansion section is greater during extension or contraction of said joint than is the rate of change of curvature of the side of said joint adjacent to said expansion section.   
     
     
       4. The expansion joint of claim 3 wherein said tubular connector is comprised essentially completely of flexible sheet fabric material. 
     
     
       5. The expansion joint of claim 3 wherein said tubular connector has a substantially rectangular shape. 
     
     
       6. The expansion joint of claim 3 wherein said tubular connector has a substantially square shape. 
     
     
       7. The expansion joint of claim 3 wherein said expansion sections are of substantially equal dimensions.